Jump by Van Halen playing
In Wade's hideout there's a Nintendo lunchbox (haven't managed to catch the game)
There's also a crushed Carl's Jr cup
There's a bunch of stickers near these but I've only made out the GSS sticker so far
Entering the Oasis, we first see Minecraft World
Henry and Em's house from The Wizard of Oz flying around in Hurricane World
1989 Batman climbing on Everest
Planet Ludis flashes by, a reference from the book which is otherwise almost completely absent from the movie
DC's The Flash
Ray Harryhausen Cyclops from the 7th Voyage of Sinbad
Borg? (off to the left of the cyclops)
BattleToads?
RoboCop
Marvin the Martian
Mortal Combat guy? Can't figure this one out - right before Parzival changes his hair
Sonic the Hedgehog lining up for the gate
Tracer from Overwatch
Hello Kitty, Badte-Maru, and Keroppi
First zooming in on Planet Doom, it looks like a battle between giant scorpions and pegasai possibly from Clash of the Titans?
Freddy Kruger
Duke Nukem
Some kind of Smiley Face guy
EM-1 Rail Gun from Eraser
Blob?
Raynor from StarCraft
Donkey Kong Jr poster on the wall behind the girl
Jason Voorhees
Everybody Wants to Rule the World by Tears for Fears
World of Warcraft female orc?
There's a guy behind the orc that looks like one of the Daft Punk guys but he turns his head and it almost looks like a skull with a helmet on
Doc Brown, back from the future outfit, Back to the Future
Movie note: 1972 is the mint date on the quarter in focus on Halliday's right eye and is also Halliday's birthday. The quarters in the book were minted in 1984 but no reason is given for this date.
In the funeral scene, Halliday is wearing a Simon pin on his lapel
Halliday's funeral is a Star Trek themed funeral
Halliday's casket is a MkII photon torpedo from Star Trek II which is draped with a flag of the Federation of Planets similar to how Spock's casket appeared at the end of the same movie.
Halliday sits up in his casket - this seems to mimic Dracula sitting up in his coffin in the old Beli Lugosi Dracula movies but I can't find a reference